For the sake of transparency, let's begin today's post with some failure. I stayed up 'til about 5am last night fabricating a spigot for this FCR-MX carb I want to run...
Everything was looking good. Got good transition to the head. Good fit between the carb and the intake. The Rotax boot was a good fit, too. I was proud.
Then, I go to install the carb in the frame and lo and behold, the throttle mechanism interferes with the frame. Damn. So, back to the computer and I order a boot from Jet's R Us that will be much shorter than what I have here. Hopefully, it fits inside of the frame being at least 10mm closer to the head.
An aluminum DR500 swing arm arrived in the mail yesterday via BradJ, through Mr E and originally from Kanticoy. It's like sharing a village girl around here. I hoped the swingarm would be super easy and straight forward, but of course it was not. It wasn't too hard, though, either.
Fortunately, the OD of the DR370 bushings match the OD of a 91 RM125. I happen to have the rear swing arm from a 91 RM125 that I wasn't able to sell at the last two Mid-O's. The DR500 and the 91 RM 125 share the same swing arm pivot axle dimension. So, I replaced the outer DR375 Swing arm bushings with the outer bushings from the RM. Because the RM is mono shock, it also has inner bushings. I trimmed the inner bushings down 10mm,
reamed the frame plugs to match the OD of these bushings and voila, an aluminum swing arm on a DR370. The rear axle was a pretty easy fit. Some things needed trimmed to fit through the DR500 axle slots, and the frame brake cable stay has to to be moved, but otherwise pretty mundane stuff. Of note, I will ultimately weld in the frame plugs once the rest of the bike is sorted.